This invention relates generally to using silica in poly(arylene sulfide) compositions to reduce drool. This invention relates more particularly, but not by way of limitation, to using a limited quantity of high surface silica in a highly mineral filled poly(phenylene sulfide)/fiberglass composition to improve shear sensitivity of the composition so that it does not drool when injection molded.
Injection molding is a process by which molded shapes are made by injecting a measured quantity of molten material into a die. Undesired molding can occur if the molten material continues to flow even after the inlet flow has been shut off. An unwanted amount of this continued flow is called drool. One way to stop drool is to use shut off nozzles, but not all molding processes use these; therefore, there is the need for an improved material which flows adequately to be injection molded, but which does not continue to flow adversely (i.e., drool) after molding pressure has been released.
Various types of materials can be injection molded. One type is a thermoplastic composition containing arylene sulfide polymer [referred to as poly(arylene sulfide)]. A particularly useful species of poly(arylene sulfide) is poly(phenylene sulfide). A specific poly(phenylene sulfide) composition which can drool when injection molded comprises about 35 percent by weight Ryton.RTM. PR07 poly(phenylene sulfide), about 35 percent by weight fiberglass, about 28.75 percent by weight talc or calcium carbonate, about 1 percent by weight lithium carbonate and about 0.25 percent by weight polyethylene. Another specific poly(phenylene sulfide) composition which can drool when injection molded comprises about 38 percent by weight Ryton.RTM. PR07 poly(phenylene sulfide), about 35 percent by weight fiberglass, about 25.75 percent by weight calcium sulfate, about 1 percent by weight lithium carbonate and about 0.25 percent by weight polyethylene.
Because injection molded thermoplastic products containing poly(arylene sulfide) have a wide range of uses, it would be desirable to provide poly(arylene sulfide) compositions which do not drool when injection molded. More specifically, it would be desirable to provide modified versions of the aforementioned poly(phenylene sulfide) compositions which do not drool when injection molded.